How much it costs isn't much of a factor for super powers. It doesn't stop nations spending millions upon millions for this research, I also highly doubt any war would completely leave us extinct, we've gotten this far through some of the worst shit and it isnt stopping, sure some if us is thriving and surviving but were here and still growing in numbers everyday.

Unrelated but Ithink in 40k humans are abundant as ants, we just keep coming.

Also Fallujah was is a good example of bombing, they'll warn you weeks notice if you arent Insurgent get the fuck out, but those who stayed got bombed for an entire week. Americans don't need there infrastructure, it had it's golden age but it's all useless now so they gave no fuck and tore that place asunder, but large cities like Hong Kong, Seoul, Vancouver BC, new York and such are worth billions upon billions why waste that?

Also for bots now, humans have that quest of self preservation, now imagine being able to be in both body andthe net. I think Asimov is slightly wrong and Shirow Masamune of Ghost In The Shell is actuallyon to something, we may develope an ever recoding system, in other words learning like a child, it sees and will ry to emulate it may not have a soul but the thing can think and may care not because of it's initial programming which is long gone but through experience.